RFC: Add a rule where every PR should include body text

[orta]

Proposal:

It's possible to make a PR without any additional context. We should request that anyone making a PR with an empty body should add some text.

Reasoning

PR metadata is an important part of understanding how/why something happened later on, skipping a writeup or a quick link to a slack conversation makes it much harder to grok Artsy as a collection of systems.

Exceptions:

None that I can think of today? I was wondering about a revert PR, but even those could do with a "why".